Advertisement

Advertisement

Physicists mourn as hinted particle vanishes in leaked LHC data

Nothing to see here

Everett/REX/Shutterstock

By Leah Crane in Chicago

For nearly eight months, physicists have been waiting for confirmation of a potential new particle that could change our entire view of physics. Now it seems the hinted particle was nothing more than a statistical blip.

In December 2015, the ATLAS and CMS collaborations at CERN announced that they had each found a bump in their data at an energy of 750 gigaelectronvolts (GeV): an excess in the number of photon pairs produced inside the Large Hadron Collider, compared with predictions from the standard model of particle physics.

A week after the announcement, theorists had written over 100 possible explanations; today, there are over 500. Nearly all of these papers posit the existence of a particle with a mass of 750 GeV or higher whose decay created the extra photons. Because this particle would have been outside the standard model of particle physics, it could have forced a reconsideration of how particles and forces interact.

Advertisement

Sadly, it seems that the 750 GeV particle wasn’t meant to be. Physicists at the International Conference on High Energy Physics (ICHEP) in Chicago were due to reveal the latest data on the excess of photon pairs at 750 GeV later today, but a paper accidentally posted online last night by the CMS collaboration states that their new round of data found no extra photons. This suggests the earlier hints were just a statistical fluke.

Statistical fluke

“As data comes in, excesses tend to come and go,” says CMS researcher Nadja Strobbe at Fermilab, near Batavia, Illinois. Researchers from ATLAS are due to present their results later today, but rumours suggest they will announce that the 750 GeV bump is gone.

The loss of the supposed particle means theorists now have nothing to guide them in the search for physics beyond the standard model, and must wait for the next bump from the LHC. We know the standard model is incomplete as it has nothing to say about dark energy or dark matter, which make up 95 per cent of the known universe, so something else must be out there.

“We have just started the hunt,” says CMS spokesperson Tiziano Camporesi. “We could achieve it by the end of this year, by the next two or three years, but there is still the possibility that it could take longer.”

The discovery of the Higgs boson in 2012 was celebrated, but hasn’t helped push particle physics on, as its properties were exactly as predicted. “It is the standard model exactly like it was ordered, this feels like something my parents or my grandparents wrote down, and so far nature is delivering exactly that, which is sort of fantastic, and sort of very frustrating,” says former ATLAS researcher Adam Gibson at Valparaiso University, Indiana. “Apart from the Higgs, this is the most exciting bump that we’ve had at the LHC, but I think a lot of us thought there was a fair chance it was just a statistical fluctuation.”

Excitement over the 750 GeV bump may be just about over, but particle physicists soldier on, scouring the data for bumps that might illuminate surprises. “What’s next is to continue to do the work which we are doing as best as we can,” says Camporesi. “[Non-standard model physics] will be discovered, if it is there.” This result may have been negative, but the prevailing attitude at ICHEP seems to be that it’s just a matter of time.